The invention relates generally to mechanical devices for plugging or stopping pipes, tubes and like fluid flow conduits. More particularly, the present invention is concerned with devices for plugging condenser tubes used in power generation systems and like systems wherein the plug is subject to moderately high positive and negative pressures (100-200 psi) and system vibrations. Heretofore, it has been known to employ tube plugs in such condenser environments wherein the devices comprise expandable rubber or like elastomeric sleeves to effect a liquid seal against the tube wall. These devices also include extensible mechanical gripper elements which are axially engaged by the sleeve at one end to radially expanded the grippers and frictionally contact the tube sidewall to resist the system fluid pressure and maintain the plug in the desired location. These prior plug devices are not entirely satisfactory since, over a period of time, the resilient elastomeric sleeve materials tend to soften which leads to a decrease in the axial and radial forces imposed on the gripper elements. Continued system vibration and fluid pressure eventually leads to plug loosening and failure. It has been observed that the mechanical grippers of such prior plug devices may become loosened by system vibration due to the fact that the grippers are held in an expanded state at one end by the resilient sleeve and at the other by a threaded nut. This prior arrangement does not afford a positive lock for the nut since the rubber or elastomeric sleeve material is inherently nonrigid.
The present invention solves these prior problems by providing a high confidence tube plug for use in condenser tubes or the like which will resist loosening even if the resilient fluid sealing sleeve should soften over time. The present invention also provides a superior tube plug for high pressure condenser tubes in power generation systems and the like which includes a positive rigid mechanical stop for the gripper elements to resist system vibrations so as to yield a long and reliable service life.